import java.util.Scanner;

/**
 * If there are no bugs, it was created by Chen FengYao on 2018/4/2;
 * Otherwise, I don't know who created it either
 */

public class Question1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        // 0 => 0
        // 1 => 0 + 1
        // 2 => 0 + 1 + 2
        // 3 => 0 + 1 + 2 + 3 + 4
        // 输入几 就 0 + ... + 几
        int sum = 0;
        for (int i = 0; i <= num; i++) {
            sum = sum + i;
        }
        System.out.println(sum);

    }
}
